gc: fix SIGBUS

R=ken2
CC=golang-dev
https://golang.org/cl/1906042

include/u.h

@@ -68,6 +68,7 @@ extern "C" {
 #include <stddef.h>
 #include <math.h>
 #include <ctype.h>	/* for tolower */
+#include <signal.h>
 
 /*
  * OS-specific crap
@@ -192,6 +193,10 @@ typedef u64int uint64;
 #undef _NEEDUINT
 #undef _NEEDULONG
 
+#ifndef SIGBUS
+#define SIGBUS SIGSEGV /* close enough */
+#endif
+
 /*
  * Funny-named symbols to tip off 9l to autolink.
  */

src/cmd/gc/go.h

@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 #include	<u.h>
-#include	<signal.h>
 #include	<libc.h>
 #include	<bio.h>